On the steady-state and dynamic characteristics of bipolar transistor power switches in low-loss technology

To achieve loss reduction in large power switches based on bipolar transistor technology, the injection of a compensating voltage into the Darlington loop is investigated theoretically and experimentally for several configurations. The theoretical model predicts that a total loss reduction of 50% in the steady-state could be possible in comparison to conventional Darlington and directly-driven single bipolars. Experimental measurements on a power switch configuration for realising all three types of switches compared theoretically bear out these expectations. The complications of the technology to achieve this compensation, as well as the influence on turn-on and turn-off, are subsequently evaluated. It appears that simple solutions for realising the compensation by high-frequency Royer oscillators are feasible, and the compensation does not affect turn-on time or falltime. Turn-on and turn-off technology as developed for single bipolars and Darlingtons achieves the same results in the compensated Darlington power switch. The storage time corresponds to what is found for single bipolars. It is concluded that the compensated Darlington high-current power switch is a viable possibility for application in convertors where low losses are combined with requirements for fast turn-on and turn-off.